Handle duplicate headers and changing number of data columns.

[dcslagel]

Description:

Handle duplicate headers and changing number of data columns.
This pull-request enables parsing some of the LAS files in issue:

• more malformed LAS files from USGS to handle, mostly florida more malformed LAS files from USGS to handle, mostly florida #61

Changes to dist/index.js:

• Only read a required unique header and its data once.
  Ignore additional entries for the unique header.
  These are the headers: ~V, ~W, ~C, ~P, ~O, and ~A.
• Move the inital parsing from las string data in interim structured
  section data to sub-function: las2json.readSections()
• Move las2json sub-functions to the bottom of the section to make the
  main logic more prominent.
• Handle cases of data sections that have an inconsistent number of data
  columns in the data rows. If a row has more data columns than the
  headings, then add generic colunms titled 'UNKNOWN' + a number. Then
  populate the previous rows for that column with zero string values '0'

Add tests:

• dist/test/las2json/test_duplicate_header.js
• dist/test/las2json/test_extra_data_columns.js

This is a fairly big change, with moving some code sections around and replacing some code with a sub-function.

Test Results:

npm run test-las2json
...
1..50
# tests 50
# pass  50

--

Let me know if this change could be accepted (or rejected) or
needs some additional changes to be approved and merged.

Thank you,
DC

[JustinGOSSES]

Sorry I've been slow on this one. Will try to review this within the week. As you say, it's a bigger change than normal, so want to give it a good review.

[JustinGOSSES]

Looks good. Read through it and ran all tests.

Unfortunately, I'm left this sit too long and now there's some conflicts with newer pull requests. Hence, I've left some old code in but commented it out. Will go back in and delete the commented out code after a while if no problems in use as well.